There are cases where you need to store private keys in a secure computer, or maybe do offline signing of cryptocurrency transactions. However, there is a barrier when copying data to an offline device and that is it's offline. Using email is out of the question and even USB might be a security risk. I put together this offline QR generator and webcam reader a while ago but that is a bit boring isn't it? The new application is using speaker audio and send any message to the receiver who intercept with a microphone. I also put in strong encryption for the most paranoid users.
- Demo site: https://joohansson.github.io/offline-audio-messenger/
- Source code: https://github.com/Joohansson/offline-audio-messenger
It can be used in any modern browser supporting webassembly either online or downloaded and run offline (with or without a web server). Even iOS (safari) and Android works. For testing, you can either record the audio with your phone and playback to the same window or use two browser windows and send between them.
No message data is shared and the source code (and hosted source code in gh-pages branch) can be reviewed above.
The audio protocol comes from https://chirp.io/
Please let me know if you find any bugs or find it useful.